On Thu, 26 Sep 2024 15:13:07 +0900
Tatsuya S<tatsuya.s2...@gmail.com> wrote:
A extra entry is shown on stack trace(CONFIG_UNWINDER_ORC=y).
[003] ..... 110.171589: vfs_write <-__x64_sys_write
[003] ..... 110.171600: <stack trace>
=> XXXXXXXXX (Wrong function name)
=> vfs_write
=> __x64_sys_write
=> do_syscall_64
=> entry_SYSCALL_64_after_hwframe
OK, I confirmed it;
------
echo 1 > options/func_stack_trace
echo "vfs_write" >> set_ftrace_filter
echo "function" > current_tracer
echo > /dev/null
cat trace
sh-136 [005] ..... 266.884180: vfs_write
<-ksys_write
sh-136 [005] ..... 266.884188: <stack trace>
=> 0xffffffffa0004099
=> vfs_write
=> ksys_write
=> do_syscall_64
=> entry_SYSCALL_64_after_hwframe
------
To resolve this, increment skip in __ftrace_trace_stack().
The reason why skip is incremented in __ftrace_trace_stack()
is because __ftrace_trace_stack() in stack trace is the only function
that wasn't skipped from anywhere.
Signed-off-by: Tatsuya S<tatsuya.s2...@gmail.com>
---
kernel/trace/trace.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index c3b2c7dfadef..0f2e255f563c 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2916,10 +2916,8 @@ static void __ftrace_trace_stack(struct
trace_buffer *buffer,
* Add one, for this function and the call to save_stack_trace()
* If regs is set, then these functions will not be in the way.
*/
Hmm, with this change, the above comment should also be updated.
-#ifndef CONFIG_UNWINDER_ORC
- if (!regs)
+ if (IS_ENABLED(CONFIG_UNWINDER_ORC) || !regs)
skip++;
-#endif
Also, this solves just one pattern (only enable function tracer) but if
there are fprobes (or kprobes) on the same function, it introduces
another issue.
e.g. (with this fix)
------
echo 1 > options/func_stack_trace
echo 1 > options/stacktrace
echo "vfs_write" >> set_ftrace_filter
echo "function" > current_tracer
echo "f:myevent vfs_write" > dynamic_events
echo 1 > events/fprobes/myevent/enable
echo > /dev/null
cat trace
...
sh-140 [001] ...1. 18.352601: myevent:
(vfs_write+0x4/0x560)
sh-140 [001] ...1. 18.352602: <stack trace>
=> ksys_write
=> do_syscall_64
=> entry_SYSCALL_64_after_hwframe
sh-140 [001] ...1. 18.352602: vfs_write
<-ksys_write
sh-140 [001] ...1. 18.352604: <stack trace>
=> ftrace_regs_call
=> vfs_write
=> ksys_write
=> do_syscall_64
=> entry_SYSCALL_64_after_hwframe
------
As you can see, myevent skips "vfs_write".
(and function tracer still have ftrace_regs_call() )
